Or: (3) there are advanced races out there that know we exist, but have no interest in talking to us. ~ Modernman
Or: (4) planets are very bad places, they have diseases, nasty natives, a deep gravity well, and poisonous atmospheres as often as not. Stick to the asteroids, they're sterile, easy to get to, easy to leave, and have all the resources you really need...
Sure a race or two may "feel" this way, but it ridculous to assume we don't see evidence for intelligent life, objectively, because every intelligent species likes the "asteroids".
Unless the aliens are genocidal xenophobes, there would be no reason for an advanced species to contact us. I'd postulate that for a species to survive to a point where they can master space travel, perhaps FTL, they need to develop some sort of moral/ethical code that will prevent them from wiping themselves out. We came pretty close, as a species, to wiping ourselves out through nuclear war. If we'd been, say, 10% more aggresive as a species, the Earth might very well be a nuclear wasteland right now.
So, unless the alien species is genocidal towards other species, their only interest towards us would be to study us, much like we study chimps or gorillas. I'm not aware of any special properties our planet has, so I doubt they'd be interested in our resources. Imperialism or slave labor? (like in Battlefield Earth) Highly doubtful that an advanced, space-faring race would have any interest in that- they can obtain all the resources they need by mining asteroids and such with robots.
The only other interest they might have in us would be as some type of culinary delicacy. However, if that was the case, it would be much simpler for them to abduct members of our species covertly and establish a human livestock breeding program on their home planet.